How do I export all contacts (names and phone numbers) to a text file on SD card offline?

It is function integrated into build-in Contacts app.

1. Open Contacts


2. Switch to "Contacts" tab


3. Press the tree-dots button at the bottom


4. "Import/Export"


5. Export to storage


6. Check all checkboxes


7. Check file like 00002.vcf

This is a vCard file. One can manually open it in a text editor and search for contact names and phone numbers even if no special program for vCard is installed.